1. Field of the Invention
The present invention teaches new and useful compositions for the measurement of free or unbound analyte concentrations in a fluid. The present invention includes the use of capture ligands and stabilizing agents to improve the accuracy of analyte concentration assays. Methods and tools for using the present invention are also disclosed.
2. Background Art
Various assays have been developed to measure the concentration of an analyte in solution. For example, assays have included mixing a solution containing an analyte with a capture ligand, washing away any impurities, and then measuring the analyte associated with the capture ligand. Several technical difficulties exist with these detection methods. In some instances, unintended binding of impurities to the capture ligand occurs. Additionally, in some instances the binding of the analyte to the capture ligand is not stable and the analyte disassociates from the ligand. In some instances, the analyte in a solution can exist in a bound form (e.g., bound to a protein) and an unbound form, and it may be desirable to only measure the concentration of the unbound form. Thus, in some instances it is necessary to stabilize the equilibrium between bound and unbound forms in order to obtain an accurate and reproducible measurement of analyte concentration.
To address these problems, Beckman Coulter, Incorporated (BCI, Fullerton, Calif.) has traditionally used an alkyl amine fluoro-surfactant (FC100, manufactured by 3M Corporation, St. Paul, Minn.) in BCI's various analyte concentration assays. FC100 is a complex cocktail of amine fluoro-surfactants that exhibits substantial lot to lot variability in its exact chemical composition. According to 3M Corporation's Material Safety Data Sheet (MSDS, issued Feb. 8, 2000, Document Number 10-3799-3), FC100 contains water, diethylene glycol butyl ether, fluoroalkyl sulfonate sodium salt, and a trade secret mixture of residual organic fluorochemicals. Without being limited by theory, the inventors believe that an alkyl amine fluoro-surfactant facilitates the accurate determination of the amount of free unbound analyte versus bound analyte present in a sample solution by stabilizing the equilibrium and therefore allowing for accurate measurement of analyte concentration.
Several years ago, the Environmental Protection Agency of the United States expressed concern regarding certain fluorocarbon compounds, such as fluorocarbon octanoic acid and its derivatives, as potentially hazardous compounds. Therefore, a need exists for an alternative to replace the alkyl amine fluoro-surfactant with a different assay composition that can function in determining analyte concentration.
The present invention provides novel compositions as well as methods and kits for using those compositions in assays to accurately measure the free unbound analyte in a sample from a subject.